Leak monitor for hydraulic drive systems

ABSTRACT

The drive systems include at least one conduit leading to a machine unit which may be selectively connected to a pump or a tank. Arranged in the conduit is a holding valve which, when the conduit is connected to the tank, maintains a minimum pressure in the conduit branch leading to the machine unit. A pressure sensor arranged in this conduit branch determines the actual value of the conduit pressure. If this decreases with respect to the minimum pressure predetermined by the opening pressure of the holding valve, which is determined by a comparison device, this is an indication that the conduit section has a leak, if only a small one.

The invention relates to a method of operating a hydraulic machine unitwhich is selectively connected to a tank or a pump via at least oneconduit. The invention further relates to a hydraulic drive system,particularly for working machines used in underground mine operations,with a tank, a pump connected thereto and conduits leading to a machineunit for the supply and return of the hydraulic fluid, the conduitsstarting from a control device.

With hydraulic drive systems for working machines used in undergroundmine operations there is the problem that on the one hand damage to theassociated hoses occurs relatively frequently because the hoses aresubjected to external forces under the conditions which prevailunderground and that on the other hand the damage to the hoses may onlybe detected and located with difficulty because the hoses are notvisible or accessible or only with difficulty either in the vicinity ofthe working machine itself or as a consequence of the prevailingoperational conditions.

If, for instance, the above problem is considered in the case of aso-called boom-type road header as a road header, the result is, inparticular, a loading, which is absolutely typical for the conditionsunderground, of the machine units by the heap of debris which has beencut free and which reaches the partially exposed hoses and causes anexternal mechanical stressing of the hoses. Additionally, the hoseswhich are guided partially covered in or on the machine body are alsoinvolved since the boom-type road header also moves and operates in theheap of debris so that portions of the debris also reach the hosesguided in the vicinity of the machine.

Whilst hose breakages which occur may be relatively easily detected as aresult of the hydraulic fluid which visibly escapes at high operationalpressure in the drive system and above all may be located in accordancewith its escape, there is a considerable problem in the detection ofsmaller leaks which can be scarcely detected and located as such evenduring operation of the machine. Thus such small leaks occur unnoticedeven during idling of the drive unit or the machine during which anidling pressure in the hydraulic system of the order of, for instance, 3bar can be assumed, also during working sequences at the machine asregards all units not involved therewith and thus not subjected to theoperational pressure because a functional failure of the units inquestion does not occur. Such small leaks are thus frequently onlypresumed or detected as a result of establishing an above average"consumption" of hydraulic fluid and can only be cured during a stoppageof the machine.

The problem of leakage losses is however not limited to the workingmachines discussed above and used in underground mine operations butapplies basically to all units driven with hydraulic fluid. In eachcase, leakage losses impair not only the efficiency of operation butalso constitute an environmental load which should not be underestimatedsince the hydraulic fluids are to be regarded as aggressive pollutants.

It is thus the object of the invention to provide a hydraulic leakmonitor with which even small leaks in the conduit system of therelevant working machine may be detected.

The solution of this object together with advantageous embodiments andfeatures will be apparent from the content of the claims which precedethis description.

The invention is based on the recognition that the stoppage times of themachine units in which they are switched off or are temporarily notacted on by the working pressure can be used to ensure the tightness ofthe conduits. For this purpose, a minimum pressure is set in theconduits which is at least at the level of the biassing pressurepredetermined by the hydraulic system. This means that the conduitcannot discharge to the tank any further than to the predeterminedminimum pressure. If, however, the pressure within the conduit sinksbelow the minimum pressure, this is an indication that a leak hasoccurred. Even slight leakages may thus be detected and located early. Aserious conduit breakage with corresponding loss of hydraulic fluid andwith corresponding evironmental loading can thus be prevented.

The invention starts from the basic concept that disposed in eachconnecting conduit to a machine unit there is a holding valve with anopening pressure set to correspond to at least the biasing pressureprevailing in the conduits during idling of the machine and a pressuresensor between each holding valve and the machine unit, whereby themeasured value is transmitted to a device for comparing the actual valuewith the opening pressure which is predetermined as a desired pressurevalue.

The invention is principally associated with the advantage that evenrelatively small leaks can be determined with the measurable pressuredrop in the region of the hoses, even during idling of the machineoutside the functional controls of the machine unit in question. Thepossibility is thus advantageously obtained of replacing even onlyslightly damaged hoses or conduits in the course of preventativemaintenance and thus avoiding a complete hose breakage and the stoppageof the machine necessarily associated therewith. A further advantage isthat even during the course of working processes of the machineindividual hoses or conduits which are not subjected to the operationalpressure can be replaced since all the hoses not connected to unitsinvolved in the working process of the machine are cut off from thebiasing pressure by the holding valves so that they can thus be replacedeven during further operation of the machine. This advantage is also ofgreat significance in the context of preventative maintenance.

In order to detect and locate small leaks it is sufficient to expose thecheck valves to a pressure which corresponds to the biasing pressureprevailing in the conduits during idling of the machine so that onlywhen the machine unit connected to the hydraulic hoses in question isswitched on are the hoses subjected to the operational pressure which isthen to be applied, whereby when the operational pressure is applied theholding valve opens the path for the hydraulic liquid.

If the machine unit is not subjected to operational pressure, thebiasing pressure, which is determined by the sensors disposed in thehose system, prevails in the associated hose system. An actual value isthus available which must correspond to the set desired value in theamount of the biasing pressure when no leak is present. If thecomparison of the predetermined desired value in the amount of thebiasing pressure with the actual value determined by the sensor for thepressure prevailing in the hose system produces a deviation in the senseof a pressure loss in the hose system, this pressure loss can only becaused by hydraulic fluid discharging via a leak. This deviation of thedesired/actual values can then be converted by the device into anacoustic and/or optical signal for fault detection.

In exemplary embodiments of the invention it is provided that aplurality of holding valves with associated sensors are disposed to formconduit sections in order to facilitate the location of leaks; the sameapplies to machine units connected in a compound arrangement by means ofbranch conduits in which a holding valve with a sensor should then bearranged downstream of each junction.

The invention uses valve devices which can be used on a multiplicity ofany desired hydraulic machine units but particularly on double-actingworking piston machines, each of which requires two conduits. Thepreferred field of application is, as mentioned, such devices in whichthe conduits or hoses are concealed and/or subjected to externalinfluences, such as in excavation work in road building and particularlyin mines.

The valve devices can provide a separate valve unit for each conduit.They are, however, then heavy, cost intensive and space consuming. Inaccordance with the invention, a valve device is provided which islighter and smaller and which may be manufactured more economically.

To this end, the valve device in accordance with the invention ischaracterised in that it constitutes a plate-shaped block in which thebranches of each conduit extend at an angle to one another towards theassociated check valve whereby the branches leading to the controldevice pass into mutually opposing narrow sides of the block and thebranches leading to the hydraulic machine unit pass into a common thirdnarrow side of the block and whereby further the branches of the firstconduit are offset with respect to one another relative to those of thesecond conduit both in the direction of the mutually opposing narrowsides and also transversely to the plate-shaped block.

Such an arrangement of the individual conduit branches and components inand on the plate-shaped block ensures a minimum constructional size. Theblock may also be machined and prepared in a small number of workingsteps so that the manufacturing costs can also be minimised.

These advantages can be reinforced if the branches of each conduitextend at right-angles to one another, whereby the same branches of thetwo conduits preferably extend parallel to one another.

The holding valves can be installed in openings which extend transverseto the plate-shaped blocks. On the other hand, it is more advantageousif the holding valves are inserted into bores in a fourth narrow sideopposed to the third narrow side. These bores represent only a slightlyincreased amount of work, particularly if they constitute continuationsof the branches leading to the machine unit.

The arrangement of the pressure sensors may be of any type. Preferably,however, the pressure sensors are arranged at one of those narrow sidesinto which at least one of the branches leading to the control devicepasses. They can then be disposed in a favourable manner adjacent to oneanother on the block.

Such combinations of the features mentioned above which differ from theabove combinations are also disclosed as being of importance to theinvention.

The invention will be described in more detail in the followingpreferred exemplary embodiments in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a schematic representation of a hydraulic drive system and itsassociated components;

FIG. 2 is a front view of a valve device in accordance with theinvention; and

FIG. 3 is an associated side view, seen from the right in FIG. 2.

Rigidly cased conduits 13 extend on a control device 10 with a pump 11and a tank connection 12 to connections from which conduits 14,15,constructed as hoses, extend to a machine unit 16 which is shown as anexample; in the case of a boom-type road header as the working machinethe machine unit 16 can, for instance, be the loading apron side platecylinder on the loading apron of the boom-type road header.

Connected into the conduit 14 and also in the conduit 15 is a respectiveholding valve 17, preferably directly downstream of the connection tothe conduits 13 of the control device 10, associated with which is asensor 18 for determining the respective pressure prevailing in theconduit 14,15, which for its part transmits the determined actual valuesfor the pressure prevailing in the conduits to a computing device 19 inwhich a comparison of the actual value with a predetermined desiredvalue is effected. Due to the alternating action on the conduits 14,15depending on the operational state of the machine unit 16, the holdingvalve 17 must be constructed to be double-acting, that is to say to actin both directions.

In accordance with the invention, the desired value predetermined in thedevice 19 can correspond to the biasing pressure produced by the pump 11during idling operation which, for instance in the case of a boom-typeroad header of usual construction, is about 3 bar. The opening pressureof each check valve 17 is also set to this pressure and opens theassociated conduits 14,15 when the biasing pressure is exceeded oncommencement of the working operation of the machine unit 16.

In the non-functional setting of the machine unit 16 the biasingpressure of 3 bar must also be present in the conduits 14,15 between theunit 16 and the control device 10 when the holding valve 17 is closed.Accordingly, if in the off position of the machine unit 16 an actualvalue is determined by the sensor 18 which is the same as the desiredvalue predetermined in the computing device 19 then there is no leak; ifan actual value is transmitted by the sensor 18 to the device 19 whichis less than the desired value then the pressure loss which is thusdetermined in the conduits 14,15 can only be caused by a leak in theconduits and by hydraulic fluid which is thus leaking so that even ifthe deviation of the desired/actual values is small the detection of aleak is rendered possible at an early stage.

A deviation of the desired/actual values thus determined in the device19 is indicated as an optical and/or acoustic signal, whereby it can beprovided in accordance with the invention that corresponding signals aretransmitted to the surface control station as a central monitoring pointfor the machines used in the underground area.

As is not shown in detail in the diagrammatic illustration for the sakeof simplicity, it is provided in accordance with the invention thatholding valves with associated sensors are connected in all the conduitsleading from the control device 10 and connected to machine units; italso falls within the scope of the invention to produce monitorablesections in long hoses by arranging check valves with associated sensorsone behind the other; a similar monitoring is produced also for conduitbranches in which holding valves and associated sensors are to beprovided behind the corresponding junctions.

The valve device shown in FIGS. 2 and 3 constitutes a plate-shaped block20 for the conduits 14 and 15 which extend in the form of hoses betweenthe control device and the hydraulic machine unit, in the present case adouble-acting hydraulic working piston machine. The conduit 14constitutes within the block 20 a branch 21 leading to the controldevice and a branch 22 leading to the hydraulic machine unit. Similarly,the conduit 15 constitutes a branch 23 leading to the control device anda branch 24 leading to the hydraulic machine unit. The branches 21 and22 of the conduit 14 and the branches 23 and 24 of the conduit 15 are incommunication with one another via a respective one of the check valves17. The branches 21 and 23 open out in mutually opposing narrow sides 25and 26 of the block 20. The branches 22 and 24 on the other hand openout in a common third narrow side 27. Constructed in a fourth narrowside 28 opposed to it are bores 29 and 30 which receive the check valve17. The bores 29 and 30 form continuations of the branches 22 and 24,respectively. The latter are constructed at right-angles to theassociated branches 21 and 23, respectively. Connected to the branches22 and 24 are the sensors 18. The branches 21 and 23 on the one hand and22 and 24 on the other hand extend parallel to one another.

The arrangements--with the exception of the sensors 18--are constructedoverall mirror symmetrically to one another and offset from one anotheron the one hand in the direction of the narrow sides 25 and 26 and onthe other hand transversely to the plate-shaped block 20. The latter isapparent most clearly in FIG. 2.

In this manner a simply manufactured, compact and correspondinglylight-weight and space-saving arrangement is achieved which fullfils thenecessary functions. If one of the branches 22 and 24 leading to themachine unit is not under operational pressure, the associated holdingvalve 17 sets the predetermined pressure in this branch. As soon as theassociated sensor 18 notes a reduction in the set pressure, this is anindication that the monitored hose has a leak. Each holding valvecorresponds in its function to a pair of oppositely acting back-pressurevalves which are set to a predetermined pressure.

Modifications of the described embodiment are of course possible withinthe scope of the invention. Thus the mirror-image arrangements can bereversed. Furthermore, the angles between the branches 21 and 22 or 23and 24 can be other than right-angles. The same applies to the conduitsections leading from the sensors 18 to the branches 22 and 24. Thesensors 18 need also not be situated on a common narrow side and theycan also be recessed in the block 20. Finally, it is stressed that theblock 20 certainly need not have a rectangular shape. Instead, thenarrow sides can be at any desired angle to one another and alsoconstituted by individual sections inclined to one another.

The features of the subject matter of these documents disclosed in theabove description, the claims, the abstract and the drawings can be ofimportance both individually and also in any desired combinations withone another for the realisation of the invention in its differentembodiments.

We claim:
 1. Method of operating a hydraulic machine unit which isselectively connected by means of at least one conduit to a tank or apump, said conduit being under a residual pressure when connected to thetank during idling of the machine, characterized in that the residualpressure in the conduit is set to a desired value, that an actual valueof the residual pressure in the conduit is measured and is compared withthe desired value of the residual pressure and that a leak is indicatedwhen the actual value of the residual pressure sinks below the desiredvalue thereof.
 2. Hydraulic drive system for working machines with atank, a pump connected thereto and at least one conduit leading to amachine unit for the supply and return of hydraulic fluid, the conduitstarting from a control device, characterized in that arranged in theconduit (14, 15) leading to a machine unit (16) there is a holding valve(17) with an opening pressure set to correspond to at least the biasingpressure prevailing in the conduit during idling of the machine and apressure sensor (18) between each holding valve (17) and the machineunit (16) for measuring an actual value of the pressure in the conduit,whereby the actual value of the pressure is transmitted to a device (19)for comparing the actual value with the predetermined opening pressureas a desired pressure value.
 3. Drive system as claimed in claim 2,characterised in that a plurality of holding valves (17) and pressuresensors (18) are arranged in a conduit (14,15) leading to a machine unit(16) to form conduit sections connected in series.
 4. Drive system asclaimed in claim 2 or 3, characterised in that arranged after eachbranching of a conduit (14,15) there is a holding valve (17) with apressure sensor (18) connected downstream of it.
 5. Drive system asclaimed in claim 2 or 3, characterised in that arranged in each conduit(14,15) leading away from the control device (10) there is a respectiveholding valve (17) with a pressure sensor (18) connected to it.
 6. Drivesystem as claimed in claim 3, characterized in that a valve device isprovided for monitoring at least one first and at least one secondconduit (14,15), with which the hydraulic machine unit (16) is connectedto the control device (10), that the valve device for each conduitincludes a branch (22,24) leading to the machine unit and a branch(23,25) leading to the control device, between which one of the holdingvalves (17) is arranged which sets the branch (22,24) leading to themachine unit at a minimum pressure and when the measured value fallsbelow this one of the pressure sensors (18) produces a monitoring signaland that the valve device constitutes a plate-shaped block (20) in whichthe branches (21-24) of each conduit (14,15) extend towards theassociated check valve (17) at an angle to one another, whereby thebranches (21,23) leading to the control device pass into mutuallyopposing narrow sides (25,26) and the branches (22,24) leading to themachine unit pass into a common third narrow side (27) of the block andwhereby further the branches (21,22) of the first conduit (14) areoffset from one another with respect to those (23,24) of the secondconduit (15) both in the direction of the mutually opposing narrow sides(25,26) and also transverse to the plate-shaped block (20).
 7. Valvedevice as claimed in claim 6, characterized in that the branches (21,23;22,24) of each conduit (14,15) extend at right-angles to one another. 8.Valve device as claimed in claim 6 or 7, characterized in that the samebranches (21,23; 22,24) of the two conduits (14,15) extend parallel toone another.
 9. Valve device as claimed in claim 6, characterized inthat the holding valves (17) are inserted into bores (29,30) in a fourthnarrow side (28) opposed to the third narrow side (27).
 10. Valve deviceas claimed in claim 9, characterized in that the bores (29,30) of theholding valves (17) constitute continuations of the branches (22,24)leading to the machine unit.
 11. Valve device as claimed in claim 6,characterized in that the pressure sensors (18) are arranged on one ofthose narrow sides (25,26) into which at least one of the branches(21,23) leading to the control device passes.
 12. Drive system asclaimed in calim 2, characterised in that the opening pressurepredetermined in the device (19) as a desired value corresponds to thebiasing pressure prevailing during idling of the machine.
 13. Drivesystem as claimed in claim 2, characterised in that the device (19)causes the production of an acoustic signal at a predetermined deviationof the desired/actual values.
 14. Drive system as claimed in claim 2,characterised in that the device (19) produces an optical signal forfailure indication at a fixed deviation of the desired/actual values.15. Drive system as claimed in claim 2, characterised in that a valvedevice is provided for monitoring at least one first and at least onesecond conduit (14,15), with which the hydraulic machine unit (16) isconnected to the control device (10), that the valve device for eachconduit includes a branch (22,24) leading to the machine unit and abranch (23,25) leading to the control device, between which one of theholding valves (17) is arranged which sets the branch (22,24) leading tothe machine unit at a minimum pressure and when the measured value fallsbelow this one of the pressure sensors (18) produces a monitoring signaland that the valve device constitutes a plate-shaped block (20) in whichthe branches (21-24) of each conduit (14,15) extend towards theassociated check valve (17) at an angle to one another, whereby thebranches (21,23) leading to the control device pass into mutuallyopposing narrow sides (25,26) and the branches (22,24) leading to themachine unit pass into a common third narrow side (27) of the block andwhereby further the branches (21,22) of the first conduit (14) areoffset from one another with respect to those (23,24) of the secondconduit (15) both in the direction of the mutually opposing narrow sides(25,26) and also transverse to the plate-shaped block (20).
 16. Valvedevice as claimed in claim 15, characterised in that the branches(21,23; 22,24) of each conduit (14,15) extend at right-angles to oneanother.
 17. Valve device as claimed in claim 15 or 16, characterised inthat the same branches (21,23; 22,24) of the two conduits (14,15) extendparallel to one another.
 18. Valve device as claimed in claim 15,characterised in that the holding valves (17) are inserted into bores(29,30) in a fourth narrow side (28) opposed to the third narrow side(27).
 19. Valve device as claimed in claim 18, characterised in that thebores (29,30) of the holding valves (17) constitute continuations of thebranches (22,24) leading to the machine unit.
 20. Valve device asclaimed in claim 15, characterised in that the pressure sensors (18) arearranged on one of those narrow sides (25,26) into which at least one ofthe branches (21,23) leading to the control device passes.